Method and apparatus to reduce charge sharing in pixellated energy discriminating detectors

Abstract

A CT detector includes a plurality of metallized anodes with each metallized anode separated from another metallized anode by a gap. A direct conversion material is electrically coupled to the plurality of metallized anodes and has a charge sharing region in which an electrical charge generated by an x-ray impinging the direct conversion material is shared between at least two of the plurality of metallized anodes. An x-ray attenuating material is positioned to attenuate x-rays directed toward the charge sharing region.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates generally to diagnostic imaging and, more particularly, to a direct conversion detector capable of providing photon count and / or energy data with reduced charge sharing between pixels of the direct conversion detector.[0002]Typically, in radiographic imaging systems, such as x-ray and computed tomography (CT), an x-ray source emits x-rays toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” may be interchangeably used to describe anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-rays. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signa...

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Benefits of technology

[0014]Therefore, it would be desirable to design a CT apparatus and met...

Problems solved by technology

A drawback of such detectors however is their inability to provide data or feedback as to the number and/or energy of photons detected.

Under the charge integration operation mode, the photodiode is not capable of discriminating between the energy level or the photon count from the scintillation.

In a typical imaging application, x-rays are absorbed in the direct conversion material which results in creation of an electrical charge in the direct conversion material.

A drawback of direct conversion semiconductor detectors, however, is that x-rays absorbed in the direct conversion material near the gaps or perimeters of the anodes can result in a charge being generated therein that is shared by at least two neighboring pixel anodes.

When using charge integration electronics, charge sharing can manifest itself as crosstalk between neighboring pixels, thus rendering the electronics susceptible to electronic noise amplification and spatial blurring of the image.

When using pulse counting electronics, charge sharing can result in dividing the charge between at least two anodes, resulting in lost counts when the amplitude of the charge pulse collected in at least one of the anodes is below a discrimination threshold.

Additionally, when pulse counting, high energy x-rays can result in loss of detection quantum efficiency (DQE) by the creation of two or more counts being collected in two or more neighboring anodes, thus mis-counting the events and binning, for instance, a single high energy event as two or more low-energy events.

The mis-counting of events and binning with respect to energy will degrade the capability for material discrimination.

Another drawback of direct conversion semiconductor detectors with regard to CT imaging is that the response at the edge and corners of the direct conversion crystal is not reproducible.

The changing internal field can cause a poor detector response that can lead to a non-optimal image.

Another drawback of direct conversion semiconductor detectors with regard to CT imaging is that these types of detectors cannot count at the very high x-ray photon flux rates typically encountered w...

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